1. Field of the Invention
The present invention relates generally to object inspection apparatus and more particularly to an automatic photomask inspection method and system capable of locating extremely small defects in the transparencies of photomasks used to manufacture semiconductor devices while at the same time ignoring false defects generated by the processing electronics and/or hardware.
2. Description of the Prior Art
The subject matter of this application relates to an improvement to the automatic photomask inspection system disclosed in U.S. Pat. No. 4,247,203 and U.S. Pat. No. 4,347,001, both of which are assigned to the assigned of the present application. The entire disclosures of said patent and said patent application are hereby incorporated in full into this application and form a part of this disclosure.
In all prior art automatic photomask inspection systems, "false defects" materially affect the reliability of the inspection operation because the systems are incapable of distinguishing between real defects detected and "false defects" which appear in the system output as a result of certain types of photomask irregularities, system vibration, system optical inaccuracies, data handling errors, data storage irregularities, etc. As a consequence, inspection reliability is reduced and substantial time is lost in verifying the indicated defects so that they may be either ignored, counted or even corrected.